Generally, refrigerators are household appliances that store foods at a low temperature. An inner space of such as a refrigerator may be divided into a refrigerating compartment and a freezing compartment according to temperatures for foods stored in the refrigerator. The refrigerating compartment generally maintains a temperature of about 3 degrees Celsius to about 4 degrees Celsius, and the freezing compartment generally maintains a temperature of about −20 degrees Celsius.
The freezing compartment having a temperature of about −20 degrees Celsius is a space in which foods are kept in a frozen state and is often used by consumers to store the foods for a long time. However, in the existing freezing compartment, which maintains a temperature of about −20 degrees Celsius, when water within cells is frozen while freezing meat or seafood, a phenomenon in which water is exuded out of the cells may occur, and thus, the cells are destroyed. As a result, when cooking the foods after thawing, their original taste may be lost, or the texture may change.
On the other hand, when meat or seafood is frozen, the temperature rapidly passes through the freezing point temperature zone in which intracellular ice is formed to minimize the cell destruction. Thus, even after thawing, meatiness and texture may be renewed or reproduced freshly to make it possible to enjoy delicious dishes.
As the case stands, fancy restaurants use a cryogenic freezer that is capable of rapidly freezing meat, fish, and seafood. However, unlike restaurants that need to preserve large quantities of foods, since it is not always necessary to use the cryogenic freezer in ordinary homes, it is not easy to separately purchase the cryogenic freezer that is used in restaurants.
However, as the quality of life has improved, consumers' desire to eat more delicious foods has become stronger to lead to an increase in consumers who want to use the cryogenic freezer.
In order to meet the needs of such consumers, there has been developed a household refrigerator in which a cryogenic freezing compartment is installed in a portion of the freezing compartment. It is preferable that the cryogenic freezing compartment satisfies a temperature of about −50 degrees Celsius, such an extremely low temperature is a temperature that is not attained only by a refrigeration cycle using a general refrigerant.
Accordingly, there has been developed a household refrigerator in which a cryogenic freezing compartment is separately provided in the freezing compartment in a manner in which cooling is performed by using a refrigeration cycle up to a temperature of −20 degrees Celsius and by using a thermoelectric module (TEM) in case of cryogenic refrigeration.
However, since a temperature difference between the freezing compartment of about −20 degree Celsius and a cryogenic freezing compartment of about −50 degree Celsius is very large, it is not easy to realize a temperature of about −50 degrees Celsius by applying a structure for insulation, defrosting, cold air supply, and the like, which was applied to the design of the existing freezing compartment, to the cryogenic freezing compartment as it is.
Also, when a cryogenic freezing compartment, which occupies a space of the freezing compartment itself, is provided, since reduction in volume capacity of the freezing compartment has to be minimized, it is necessary to minimize a space occupied by the structure for cooling and circulating cold air in the cryogenic freezing compartment.
Particularly, when the cryogenic temperature is implemented using the TEM, heat exchange has to be smoothly performed both at a heat absorption side and a heat generation side of the TEM, cold air cooled by the heat exchange at the heat absorption side has to smoothly circulate, and heat exchange loss and flow loss should not occur while having a simple structure as much as possible.
Furthermore, due to the volume occupied by the TEM and related components, which are installed to achieve the cryogenic temperature, there is a possibility that a flow rate or pressure distribution in the existing grill fan assembly structure changes, and thus, the freezing in the freezing compartment is not smoothly performed.